Preparation of the Sample.—Prior to the analysis, the sample must
be thoroughly mixed by pounding in a glass mortar and passing it several
times through a fine sieve. The sample is then stored in tight vessels.
1. Alkalinity.—About 5 grams are carefully boiled for some minutes
in a 100 c.c. flask with 25-30 c.c. of N/2-liyclrochloric acid ; on cooling,
the excess of acid is titrated with N/2-alkali in presence of phenolphthalein.
The alkalinity is expressed as calcium carbonate, so that the number of
c.c. of acid neutralised, multiplied by 0-025, gives the alkalinity referred
to 100 grams of the citrate.
2. Loss of Weight at 100°.—2-3 grams are dried in a steam-oven
for about 5 hours in a weighing bottle 5 cm. wide and 3 cm. high., weighed
and again heated to constant weight. The loss of weight is referred to 100
grams of citrate, which, when pure, loses 473% of water of crystallisation,
3. Hygroscopic Water.—From the loss in weight at. 100° and the
percentage of citric acid or, better, calcium citrate (sec 6, below) in the
sample the hygroscopic moisture is calculated.
Example : A sample of citrate contains 02-.|,o% of citric ueid or 84-72% of
pure calcium citrate, and loses in the steam-oven 5'o8% of its weight. Since
100 grains of pure citrate lose 4-73 grams, the water of crystallisation lost by the
calcium citrate iu the sample will be given by
100 : 4-73 : : 84-7-2 : x
% =: 4'OO.
The hygroscopic moisture is, therefore, 5-o8-.|-oo — r-o8%.
With commercial citrates this procedure gives only approximate results,
since the other substances present may influence the loss of weight in one direor
tion or the other.
4. Ash.—'About 10 grains in a platinum dish are heated first gently
over a gas flame and then fit a red heat in a, muflle for an hour.
5. Impurities.—(a) PHOSPHATES. The citrate is sometimes adul-
terated with calcium phosphate. Part of the ash is heated with nitric
acid and the solution filtered and tested for phosphoric acid by means of
(6) MAGNESIUM AND STRONTIUM. For these the ash is tested by the
(c) QXALATES. About 8 grams are dissolved in hot, dilute hydrochloric,
acid, filtered and the filtrate made up to 200 c.c. (solution <t).
50 c.c. of this solution are diluted with distilled water, rendered alkaline
with caustic soda, and then acidified with concentrated acetic acid : no
turbidity should appear.
(d) SULPHATES. To 50 c.c. of solution a, barium chloride in slight excess
(e) TARTRATES. The remaining 100 c.c. of solution a are rendered
alkaline with potassium carbonate and evaporated to dryness. The residue
is taken up in a little boiling water and filtered, the filtrate being acidified
distinctly with acetic acid and TO vols. of 0,5% alcohol added. The. crystal-
line precipitate obtained is filtered off, washed two or three times with
alcohol and dried in a steam-oven. A very small quantity of resordnol
and a few drops of concentrated sulphuric acid are gently heated in a por-
celain dish until white fumes are emitted and a few crystals of the abover the analysis of amyl acetate sec also article by Chercheffski in Les matures